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(a) Magnetization as a function of temperature of Sm1−xSrxCoO3 (2/8 ≤ x ≤ 7/8) with magnetic field of H = 0.1 T. (b) Temperature dependence of magnetization of Sm1−xSrxCoO3 (x = 0, 1/8) with magnetic field of H = 0.1 T.
Source publication
The phase transition of Sm1-xSrxCoO3 was investigated by using magnetic and electric transport measurements. Upon Sr doping, ferromagnetic behavior was found for 0.25 ≤ x ≤ 0.75 samples with Curie temperature Tc between 160 K and 180 K. Transport measurements indicate insulator-like behavior for the samples with x ≤ 0.25, an insulator-metal (IM) tr...
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Context 1
... field (M-H) curves were measured within H = ±50000 Oe at 5 K. Temperature-dependent electrical resistivity was measured on both cooling and heating in the range of 10 K to 300 K by using a standard dc four-probe method using a CCR-type refrigerator. Figure 1 shows magnetization as a function of tem- perature with 0.1 T. The magnetization was measured in a field on heating from low temperature after cool- ing in zero magnetic field (ZFC). Zero-field-cooled (ZFC) magnetization plots for Sm 1−x Sr x CoO 3 indicated sev- eral points. ...
Context 2
... low-temperature magnetization hysteresis measurements (which are presented in Figure 2), this decrease is due to the change of coercive field, not to the spin-glass state. Figure 1(b) depicts the magnetization versus tem- perature at low Sr concentration (x ≤ 0.125). Evalua- tion of the experimental data curves indicates that the low-doped samples exhibit nonmagnetic behavior. ...
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Citations
Cobalt oxides with the perovskite structure have been investigated by many authors for their rich magnetic and magnetotransport properties. In this chapter, we describe the crystal and electronic structure, the magnetic, electrical and thermoelectric properties of these compounds, and we emphasize the role of phase separation and charge ordering in those properties. The relationships between oxygen stoichiometry and physical properties are studied. This leads to a clear distinction between stoichiometric LnCoO3/Ln1-xAxCoO3 perovskites (A = Ca, Sr, Ba) and oxygen-deficient perovskites Sr1-xLnxCoO3-δ and SrCo1-xMxO3-δ. The specific role of cationic ordering in those properties is also emphasized, as exemplified in stoichiometric ordered double perovskites and in ordered oxygen-deficient perovskites such as brownmillerites, "224" and "112" derivatives.
Sm1−xSrxCoO3 ((0.1 ≤ x ≤ 0.9), SSC) with perovskite-type structure is successfully prepared by the conventional solid-state reaction method. The phase structure, optical property, electrical conductivity and infrared emissivity are all closely related to the samarium-to-strontium ratio in the SSC system. X-ray diffraction results show that the perovskite structure has an orthorhombic symmetry for 0.1 ≤ x ≤ 0.5 and a cubic symmetry for 0.6 ≤ x ≤ 0.9. The incorporation of Sr2+ can first contribute to an increase in electrical conductivity and then to a decrease; in contrast, the infrared emissivity declines at the beginning, then rises and goes through a minimum at x = 0.5, showing a U shape. Optical reflection results show that the SSC system has a high spectral reflectance in the near infrared band, and reflectivity at 1.06 µm is lower than 0.5%, with infrared emissivity less than 0.25 in 3–30 µm infrared bands. This will satisfy the laser and infrared compatible stealth in the near, middle and far infrared bands.
SmxSr1−xCoO3−δ (SSCx) materials are promising cathodes for IT-SOFCs. The influence of Sm content in SSCx (0.2≤x≤0.8) oxides on their oxygen nonstoichiometry, oxygen desorption, thermal expansion behavior, electrical conductivity and electrochemical activity for oxygen reduction is systematically studied by iodometric titration, oxygen-temperature programmed desorption (O2-TPD), dilatometer, four-probe DC conductivity, electrochemical impedance spectroscopy (EIS) and three-electrode polarization test, respectively. Iodometric titration experiments demonstrate that the electrical charge neutrality compensation in SSCx proceeds preferably through the oxidation of cobalt ion for high Sm3+ contents (x≥0.6). However, it proceeds mainly through the creation of oxygen vacancies at x≤0.5. O2-TPD shows SSC5 possesses the highest oxygen desorption ability among the range of SSCx materials tested. The thermal expansion coefficients (TECs) are high between the transition temperature and 900°C, showing values typically larger than 20×10−6K−1. All dense materials show high electrical conductivity with a maximum value of ∼1885Scm−1 for SSC6 in air, while SSC5 has the highest electrical conductivity in nitrogen. EIS analysis of porous electrodes demonstrates that SSC5 has the lowest area specific resistance (ASR) value (0.42Ωcm2) at 600°C. Cathodic overpotential testing demonstrates that SSC5 also has the largest exchange current density of 60mAcm−2 at 600°C in air.
The structural, magnetic, and electric properties of perovskite Y 1-xSr xCoO 3-δ have been investigated systematically over the 0.6 ≤ x ≤ 0.9 range of doping. The refinements of X-ray powder diffraction (XRD) patterns at room temperature indicates that the investigated samples show a unit cell of about 2 × 2 × 4 simple perovskite cubes with I4/mmm group symmetry. An antiferromagnetic (AFM) phase is observed for a Sr doping of 0.60 ≤ x < 0.775. With a further increase of Sr content, 0.775 ≤ x ≤ 0.90, a mixture of AFM and ferromagnetic clusters may exist. No metallic behavior is observed for samples investigated in ambient conditions. The resistivity (ρ) data can be described using a three-dimensional variable range hopping (VRH) model. The density of states in the vicinity of the Fermi level for all compositions can be roughly estimated by fitting the temperature dependence of the resistivity.
We have studied the magnetic and electronic properties of Eu1−xSrxCoO3 with 0/16 ≤ x ≤ 12/16. In the Sr doping range from 2/16 to 11/16, the ferromagnetic clusters coexist spatially with an antiferromagnetic matrix. The magnetization at low temperatures strongly depends on the Sr concentration x, exhibiting a maximum near half doping, which is described in term of the double-exchange mechanism. The semiconductor-metal transition at low temperatures occurs at x between 4/16 and 5/16, which indicates that the ferromagnetic clusters coalesce, leading to a percolative metallic conduction up to the composition of x = 10/16. As compared with those of La1−xSrxCoO3 and Nd1−xSrxCoO3, Eu1−xSrxCoO3 shows a larger critical Sr concentration for semiconductor-metal transition and lower ferromagnetic transition temperatures, which is attributed to the enhanced global and local lattice distortion due to the smaller cation radius of the Eu3+ ions.
